Firearm triggers now in use are designed for either single-stage or two-stage operation only and are limited to narrow ranges of trigger pull weights and travel. Design geometry requires removal of the receiver from the stock or the trigger from the receiver to affect significant changes in either weight or pull or trigger travel.
Every user of a firearm, such as a rifle, for highly accurate target or hunting purposes has a preferred trigger pull. Substantially all known trigger mechanisms have a spring bias imparted to the trigger to resist the pulling movement of the operator. The adjustment of the compression or tension forces in the spring opposing the movement of the trigger will provide an adjustment in resisting force of the trigger to the pulling action. Some shooters prefer what is known as a two-stage pull. In the first stage, the trigger moves against a pre-selected spring resistance to a position just short of that required to release the sear and effect the firing of the firearm. At the end of the first stage pull, the trigger encounters additional resistance which indicates to the operator that it is ready for firing with minimum additional trigger travel. The extent of such first stage pull and the amount of additional resistance imparted to the trigger upon entering the second stage is a matter of choice of the firearm operator. The two stage approach provides a level of safety without the use of a traditional safety mechanism.